The invention relates to a method and apparatus for trail management in a communications network, and in particular for controlling resource availability in server trails. In particular aspects the invention relates to the modelling and determination of bandwidth resource availability and conflict determination in a multi-layered connectivity managed domain.
This invention finds application in a very wide range of communications systems and data transport networks. These include, for example, any multi-layer connection-management system or any ITU-T (International Telecommunication Union) G.805 or G.803 recommendation, including ATM (Asynchronous Transfer Mode), SDH (Synchronous Digital Hierarchy) or PDH (Pleisiosynchronous Digital Hierarchy)/Asynchronous (e.g. 34 Mbsxe2x88x921/45 Mbsxe2x88x921) systems as well as optical layers, 64 kbsxe2x88x921 (DSD, ED), frame relay or IP (Internet Protocol) systems. Although the invention is therefore very widely applicable, it will be described herein by way of example in the context of SDH systems.
ITU-T Recommendation G.803 xe2x80x9cArchitectures of Transport Networks Based on the Synchronous Digital Hierarchy (SDH)xe2x80x9d of 03/93 and ITU-T Draft Recommendation G.805 xe2x80x9cGeneric Functional Architecture of Transport Networksxe2x80x9d are incorporated herein by reference.
The SONET (Synchronous Optical NETworks) and SDH (Synchronous Digital Hierarchy) standards, which were set up respectively as a US standard and a CCITT recommendation, both employ a synchronous transfer mode (STM) which offers a large number of communications channels of fixed capacity but allows flexibility in the mix of bit rates which it can transfer.
STM uses the concept of virtual containers (VCs). A container can be handled as a unit, independently of its content, by a number of network elements such as repeaters and higher order multiplexers. Such a virtual container, that is, a number of bytes reappearing at regular intervals (125 xcexcs for STM-1), is transported in a slightly larger synchronous transport module (see FIG. 1). This module consists of 9 rows and, in the case of STM-1 (corresponding to SONET level STS-3), of 270 columns of octets.
In addition to the virtual container the module contains the information needed at regenerators and multiplexers in a Regenerator Section OverHead (RSOH) field and a Multiplexer Section OverHead (MSOH) field. The virtual container itself contains a Path OverHead (POH) field, which is only analysed by the equipment at the end of a path or trail through the network, where demultiplexing of the virtual container may be required.
The virtual container of the type VC-4 fits in the so-called Administrative Unit (AU-4) of the STM-1. The VC-4 container can also be filled with smaller types of containers, for instance, by three containers of the type VC-3, each consisting of 9 rows and 85 columns of octets. In that case the VC-4 will carry some additional administrative information regarding its content, in the form of a Tributary Unit Group (TUG-3). This decomposition process can go further, by dividing the VC-4 container into smaller containers of the types VC-2, and finally VC-1. The VC-1 has two versions; the VC-11 for 1.5 Mbit/s signals and the VC-12 mainly intended for 2 Mbit/s signals. This SDH concept allows the transfer of a large range of bit rates, including the bit rate that is chosen for handling ATM, 155.520 Mbit/s.
Data is transported across a network along a predefined client trail of a predetermined data rate supported by a predefined server trail. A trail comprises a series of link connections across links at a certain hierarchical layer of the network joined by cross-connections (subnetwork connections) within network elements (or other subnetworks) in the layer of concern.
The SDH/SONET hierarchies suggest the possibility of several different client trails, which may be of different rates, being set up within a server trail. For example, a VC4 server trail may in principle carry a VC3 client trail as well as seven VC2 client trails and 21 VC12 client trails between the trail termination points.
In this context, trail is used as a generalised term for path, circuit, section, line etc. in any connection-oriented system. The single general term trail will be used herein in this way although different specific terms may be used in different systems at different hierarchical layers. This generalised use of the term trail is in line with the definitions in ITU-T G.803. Similarly, the term trail manager is used herein to encompass any connection topology management system.
A trail is generally bidirectional and may join only two trail termination points. However trails may have much more complex topologies and join more than two termination points, optionally including multiple sources and/or multiple destinations. For example a trail for broadcast signalling may be terminated by one or two sources and many destinations.
On a network, each trail may be of any requested bandwidth, or data rate, depending on the required application and may be set up (added) or torn down (deleted) at any time. A problem therefore arises, which is how to keep an accurate map of the trails and the resource availability on the network, particularly from the point of view of the individual layers of the network architecture. This problem becomes more severe if a network contains more than one trail manager or connection manager, particularly if those managers have different views of the network at any time. Each manager can then set up trails which may conflict in their use of lower-level network bandwidth.
Although discussed above with reference to SONET and SDH standards, the same problem of resource availability and resulting conflict between entities on a network may arise in any multi-layer connection-management domain.
The invention provides in its various aspects a method and apparatus for managing trails as defined in the appended independent claims, to which reference should now be made. Preferred or advantageous features are defined in dependent subclaims.
The invention may thus advantageously provide a method and apparatus for determining resource availability and/or identifying conflicts between entities claiming resources in any system in which data are carried along trails between trail termination points and the adaptation capabilities at each end of a trail have an intersection. The invention may advantageously identify conflicts between trails arising from the allocation of, or claims for, resources. Such conflicts may arise if the intersections between the adaptation capabilities at each end of two trails are identical or overlap and the trails are allocated, or claim, identical or overlapping resources. Conflicts may arise at any point along a trail or at a termination point of a trail. For example, two trails conflict if at some point in their paths they use the same link capacity in the same layer or peer layer.
In a first aspect the invention may thus advantageously provide a method and apparatus for preventing an operator on a network from provisioning two conflicting trails across the network.
The invention may in a second preferred aspect provide a method and apparatus for supplying an operator on a network with sufficient information to allow identification and coordinated resolution of conflicts between his requirements for network connections (trails) and resource availability.
Thus, in a preferred embodiment, the invention may find particular application in a SONET/SDH system in which, for example, a VC4 resource may be decomposed, or split, into a mixture of VC3, VC2 and VC1. The TUG-structured payload of SONET/SDH is an example of a system in which the adaptation capabilities at each end of a trail may have an intersection.
Preferred aspects of the invention may allow the addition and/or removal of trails utilising resources, while advantageously monitoring conflicts between trails.
Advantageously, the invention in its various aspects may provide a generic approach to the determination of resource availability and conflict within any multi-layer connection-management domain as described above.